The present invention relates generally to an apparatus for trimming metal and more particularly to an apparatus for trimming metal that reduces defects.
Modern product design and manufacturing often utilizes a wide variety of materials. Where once low carbon steel predominated, a variety of new materials such as aluminum alloys are now being utilized. These new materials often are capable of reducing weight, increasing strength and improving product efficiency. Although such alternative materials may provide a variety of benefits in product manufacturing and design, these same materials may present difficulties when subjected to manufacturing processes originally designed for low carbon steel.
One such manufacturing area where difficulties may arise is in trimming operations. Alternative materials such as aluminum alloys can demonstrate different technological behavior due to differences in mechanical and surface properties and mass density when subjected to trimming operations. These difficulties may give rise to defects arising directly from the trimming process or arising from later operations due to effects caused by the trimming process.
One defect known to arise directly from the trimming process is the generation slivers. The generation of slivers, and similar problem finishes, is highly undesirable as such slivers may get attached to the blank surface and distributed to the dies following the trimming operation. The accumulation of slivers on both these dies and the blank surfaces can result in an unacceptable surface finish when the blank is subjected to press operations. The press operations can cause the slivers located on either the dies or the blanks to be forced into the blank surface.
Known systems for dealing with such slivers commonly focus on the removal of the slivers from the dies and the blanks rather than prevention of sliver generation. The removal of slivers from the dies and the blanks can be time-consuming and expensive. Often the cleaning of dies requires the interruption of automated stamping processes, which is highly undesirable. Furthermore, close visual inspection of a part surface finish is often required and additional metal work may be required to repair indentations caused by the slivers. These processes add to the cost and time of product manufacture and may lead to an increase in the number of parts that must be scrapped if repair is not feasible.
Another approach to the elimination slivers, has been to attempt to increase the accuracy of the alignment of the upper and lower trimming steels. One such standard, that attempts to reduce the problem, requires the gap between the shearing edges to be 10% of the material thickness or less. This standard, however, can translate into gaps of less than 0.1 mm for some sheet metals. Other approaches have further limited the gap to even smaller percentages of material thickness and thereby further decrease the gap. Unfortunately, the tolerances required by such standards often exceed the capabilities of many trim dies and can still result in the production of slivers. This may result in time consuming and expensive procedures that may still fail to eliminate the production of slivers.
A second defect that may arise directly in the trimming operation is the production of burrs. Burrs are known to decrease the quality and accuracy of stamped parts and are the sources of potential splits in following operations. Again, current standards attempt to limit the production of burrs through accurate alignment of the upper and lower trimming steels. These standards attempt to minimize the gap between the shearing edges to 10% of the material thickness. Other methods suggest even smaller reduction in gap such as 0–5% of the material thickness. Again, such tolerances may be beyond the capabilities of many trim dies.
In addition to those defects arising directly from the trimming operations, defects can arise in later operations such as hemming and flanging operations. These later arising defects often can be traced back to results from the trimming operation. Irregular trim surfaces can result in splits when the trimmed blank is later subjected to hemming or flanging. The production of these post trim defects can add to additional repair and may lead to an increase in the number of parts that must be scrapped if repair is not feasible.
Instead of attempting to repair defects after their production or reduce defects by impractical procedures, it would be more efficient and cost effective to improve the trimming process. A reduction in burr, sliver, and split production would decrease costs, reduce manufacturing time, improve surface finish and reduce scrap. It would, therefore, be desirable to have an apparatus for trimming that reduced the production of defects during the trimming process.